7 dual-screen devices you can buy now (or hopefully soon)

Are two screens better than one? In recent years, device makers have been exploring this question with mixed results.

Lenovo sold a notebook less than a year ago with a slide-out second screen, but no longer offers such a model. Other computer makers -- including ASUS, MSI and even the One Laptop per Child organization -- have presented concepts for dual-screen notebooks and tablets, but have not released actual products. The biggest success so far with the dual-screen concept has been in the area of gaming, with the Nintendo DS.

Still, there are several devices utilizing two screens that you can buy now – plus a couple more that their makers hope to bring to market soon. Here's a rundown:

This beast features two color screens each measuring 14.1-inches diagonally and weighing a hefty 5.6 pounds. Perhaps acknowledging that the field of choices for tablets is quickly becoming crowded, its makers have designed
The Kno
for use in higher academia, and their business plan appropriately markets it to this audience.

They pitch their two-screen offering as a "digital textbook" which offers e-book versions of college textbooks at about half the price of their dead tree counterparts. The Kno itself, though, isn't cheap, starting at $899. (A single-screen version starts at $599.)

Each of its screens has a 1440-by-900 resolution and a multi-touch interface. A stylus is included, which you use like a pen to scribble words or doodle on one of the screens. The operating system is based on Ubuntu. It comes with only 512MB of RAM and a processor "up to 1.0 GHz." It gets online through Wi-Fi, but there's no version with 3G. And it lacks a camera.

Want one, regardless? You'll have to sign up and be put on a wait list to buy one. Its makers claim that "there are not enough to go around."

This two-screener appears to have a bit of an identity crisis. On the one hand, it's like a netbook with a second screen in lieu of a keyboard. On the other, it's like two tablets sandwiched together. And it runs Windows 7 Home Premium (32-bit).

The two LCD screens are both multi-touch and measure 7 inches diagonally. The libretto can be used where both screens show images in portrait mode, or positioned horizontally where the images are displayed in landscape format. In this orientation, you can touch type on a virtual on-screen keyboard running on the lower screen to use the libretto W105 like an ordinary netbook.

The libretto W105 was released in August, but is presently sold out from Toshiba's Web store, despite having been priced at a hefty $1,099.99. Stock is said to have been limited, as Toshiba reportedly intended only to manufacture a limited number of them. (A few online retailers are still selling them, but your best bet may be to go on eBay to try to snag one.) Yet the fact that the libretto W105 sold so quickly suggests that there could be a worthy market for small-form factor notebooks with two screens.

Kyocera is boasting that its Echo will be the first-ever Android smartphone sporting two, multi-touch screens. One screen is stacked over the other and slides out -- the bottom screen can be used for inputting text through an on-screen virtual keyboard, or function as a control panel. Or, the device's pivot-hinge mechanism can set both side-by-side to display the same image split between them. Each screen measures 3.5-inches diagonally. One of the selling points Kyocera is using is that this smartphone's combined diagonal display size of 4.7 inches and 800-by-960 pixel resolution makes it a mini tablet as well.

The Echo
will run Android 2.2. Initially, it will be available exclusively for Sprint sometime this spring. Price will be $199 with a two-year commitment to a voice plan with data.

The cheapest version of this e-reader by Barnes & Noble that's sold primarily in their stores features a 6-inch diagonal E Ink brand screen and a rectangular, 3-inch diagonal color LCD screen set below it. This color screen is used to display thumbnails of book covers which you can scroll through horizontally and touch to open a corresponding e-book in your library stored on the device. It also shows a control panel for navigating through the
NOOK's
features and settings.

The two-screen model of the NOOK is available now for $149 for the Wi-Fi version and $199 for one that also includes 3G, with service provided free through AT&T.

Take a notebook and replace its keyboard with a multi-touch display -- add a multi-touch overlay to the main screen -- and you get this. The ICONIA is billed as a "smartbook," though with two 14-inch displays, this looks and we presume operates more like a notebook still. Its specs are like one: Windows 7 Home Premium 64-bit, Intel Core i5 processor, 4GB RAM, and 128MB graphics chipset.

The lower screen shows a virtual keyboard which looks like a real full-size one (for a standard notebook), and it can, as you'd expect, be configured into other kinds of touch-input interfaces.

The pricing and a release date for the
ICONIA
is unknown. Acer does have a landing page for it, has issued a press release, and showed off a working prototype.

Like the NOOK, these devices bring together an E Ink screen and a color LCD, but unlike the Barnes & Noble e-reader, the two displays are about the same size. The enTourage eDGe has a diagonally measured 9.7-inch E Ink display and a diagonally measured 10.1-inch color LCD. The Pocket eDGe is essentially its smaller counterpart with its E Ink screen measuring 6 inches diagonally and its color LCD at 7 inches diagonally.

The result is that the eDGe devices look like a shotgun marriage between an e-reader and a generic tablet. The resistive-touchscreen tablet half runs Android (though the site for these so-called "dualbooks" doesn't specify which version). The e-reader side can receive handwritten input from a provided stylus. The hinge mechanism can be swung open all the way so that the two screens face away from the other, and you can use either eDGe model with its screens oriented in portrait or landscape mode.

The enTourage sells for $499, the Pocket for $349. Both can be bought at a few major retailers including Staples and WalMart.

NEC showed off a prototype of this dual-screen device in January at the
Mobile World Congress 2011
. Unlike the libretto W105, the Cloud Communicator LT-W appears to be meant to be used more as an e-reader than a netbook. Like the libretto, its displays are both 7-inches diagonally measured, but with resistive touchscreens, and it runs Android (2.1 was the version on the demo prototype).

It's unknown whether the LT-W will be released (either as a consumer or enterprise device) or will end up as an unrealized design concept. (One popular gadget blog came away
unimpressed with the demo
.) Guestimates as to what a selling price could be for this two-screen Android tablet are around $500.